Stabilization of unsaturated aldehydes



ing of the aldehydes.

United States Patent 2,886,493 STABILIZATION 0F UNSATURATED ALDEHYDES John W. Mecorney, Richmond Annex, and Edward C.

Shokal, Walnut Creek, Califl, assignors to Shell Development Company, New York, N.Y., a corporation of Delaware No Drawing. Application December 24, 1956 Serial No. 630,056

5 Claims. (Cl. 202-57) This invention relates to the stabilization of unsaturated aliphatic aldehydes and relates more particularly to the stabilization of alpha, beta-unsaturated aliphatic aldehydes during their processing, transportation and storage.

The unsaturated aliphatic aldehydes and particularly the alpha, beta-unsaturated aliphatic aldehydes such as, for example, acrolein and methacrolein, are known to possess a tendency to undergo autopolymerization with the production of polymeric products even at relatively low temperatures. As a consequence of such behavior these compounds heretofore have undergone serious degradation in product quality during storage and transportation. The increased rate at which these resinous products are formed at elevated temperatures has rendered exceedingly difficult the processing of these materials.

I Since in general a substantial proportion of these resinous products are insoluble in the unsaturated aldehydes from which they are formed, equipment in which these materials are treated or processed is quickly fouled or clogged to an extent rendering practical operation exceedingly difiicult. In addition to the difiiculties encountered in attempting to carry out such processing or treating steps, the formation of these resinous products of autopolymerization results in a substantial loss of desired aldehydes.

Some degree of inhibition of autopolymerization has been achieved heretofore by the use of certain inhibitors including some of phenolic character. Inhibitors suggested heretofore generally, however, have been unsatisfactory with respect to their efficiency in suppressing autopolymeriazt ion of the unsaturated aliphatic aldehydes. The relative inefiiciency of inhibitors suggested heretofore is often attributable, at least to a substantial degree,

to their inability to function in vapor spaces of equipment and storage vessels wherein the unsaturated aldehydes are.

encountered. While the rate of autopolymerization of the unsaturated aldehydes, such as, for example, acrolein, is often retarded by the presence of certain phenolic inhibitors disclosed heretofore, formation of insoluble polymeric products on the walls of equipment, process lines and storage vessels nevertheless continues to a degree militating against efficient practical scale operation. The accumulation of insoluble polymer in the vapor space of equipment quickly plugs lines, heat exchange tubes and vessels. A further disadvantage of many of the materials suggested heretofore as autopolymerization inhibitors is their relative insolubility in the aldehydes and/ or in hydrocarbon solvents often employed in the process- A particular disadvantage of inhibitors suggested heretofore is, however, their lack of volatility. Since substantial vaporization and condensation of acrolein occurs within equipment wherein the unsaturated aldehyde is processed or treated, and in the vessels wherein the acrolein is stored, formation in substantial amount of the insoluble polymeric product generally takes place at places which are not readily accessible by a relatively non-volatile inhibitor.

Patented May 12, 1959 "ice It is an object of the present invention to provide a method enabling the more efficient stabilization of unsaturated aliphatic aldehydes during transportation, stor-- age and processing.

A particular object of the invention is the provision of an improved method of inhibiting the autopolymerization of unsaturated aliphatic aldehydes during their processing, treating, or the like, at elevated temperatures.

A specific object of the invention is the provision of an improved method enabling the more efficient stabilization of the alpha, beta-unsaturated aliphatic aldehydes during transportation, storage and processing at normal and elevated temperatures.

It has now been found that substantial improvement in the stabilization of unsaturated aliphatic aldehydes during their transportation, storage and/or processing at normal or elevated temperatures, in liquid or vapor state, is brought about by efiecting such transportation, storage and/or processing in the presence of nitric oxide (NO). Nitric oxide has been found to be a superior stabilizing agent not only because of its favorable stabilizing effect upon unsaturated aldehydes in the liquid state but because of its ability to enter the vapor spaces of equipment, lines, storage vessels, etc., to function as a highly efficient stabilizing agent for the aldehydes in such vapor space. In a preferred modification of the invention the volatile stabilizing agent for the aldehydes, that is, nitric oxide, is employed in combination with an agent of lesser volatility capable of functioning as stabilizer for the aldehydes in the liquid phase such as, for example, suitable phenolic type of inhibitors.

The invention is applied broadly to the stabilization during storage, transportation and/or processing, at ordinary and elevated temperatures, of the unsaturated aliphatic aldehydes. It is applied with advantage to the stabilization of the alpha, beta-unsaturated aliphatic aldehydes such as, for example, acrolein, methacrolein, etc., regardless of their source or origin. Comprised within the alpha, beta-unsaturated aliphatic aldehydes thus stabilized within the scope of the invention are the homologs of acrolein comprising those wherein at least one of the hydrogen atoms attached to the alpha or beta carbon atom of acrolein is replaced by an alkyl group such as for example methyl, ethyl, propyl, butyl, amyl, etc. The invention .is of particular value in the stabilization of the crude aliphatic aldehydes, obtained, for example, by controlled catalytic oxidation of the corresponding olefinic hydrocarbons. Comprised within the aldehydic materials stabilized in accordance with the invention are the aqueous solutions of the crude aldehydes obtained, for example, by the absorption of olefin oxidation products comprising unsaturated aldehydes in aqueous solvents.

Processing steps conducted at elevated temperatures during the course of which the aliphatic aldehydes are stabilized in accordance with the invention comprise any of the steps to which the crude aldehydes are normally subjected during the processing or treating thereof. Such processing steps may comprise one or more such steps as for example distillation, solvent extraction, extractive distillation, heat exchange, condensation, heating, stratification, etc.

The invention is not limited to any specific method of introducing the nitric oxide into the aliphatic unsaturated aldehyde to be stabilized. Thus, nitric oxide, or inert gas comprising it, may be bubbled through the aldehyde while the latter is in the liquid phase at ordinary or elevated temperatures. It may simply be introduced in part or entirely into the vapor space above the liquid acrolein. The nitric oxide may be brought into contact with the aldehyde before, during or after the processing or treating thereof. Nitric .oxide introduced into equipment or vessels wherein the aliphatic aldehyde to be stabilized is contained may be injected into one or more parts thereof including liquid and/ or vapor space. In a preferred method of incorporating nitric oxide stabilizer into the unsaturated aldehyde, it is introduced prior to formation of precursors of the resinous products. This may generally be accomplished by introducing nitric oxide into the aldehyde while in the crude state or into the equipment wherein the crude aldehyde is being processed or treated. Without intent to limit in any wise the scope of the present invention by theory advanced herein to set forth more clearly the nature of the invention, it is believed that precursors leading to subsequent formation of resinous materials during storage may well be formed during the processing of the unsaturated aliphatic aldehyde at elevated temperatures.

The amount of nitric oxide employed to accomplish the desired degree of stabilization may vary considerably within the scope of the invention. In general, it has been found that the presence of nitric oxide in the vessel containing the aldehyde, comprising both liquid and vapor space, in an amount ranging, for example, from about 0.001% to about 1% by weight based upon aliphatic aldehyde present is satisfactory. In general, amounts in the total confined space of the vessel as low as from about 0.001 to about 0.1% by weight based upon the aliphatic aldehyde will be found satisfactory. Greater or lesser amounts of the nitric oxide may, however, be employed within the scope of the invention. Thus, during the processing of the unsaturated aldehyde in continuous systems the continuous or intermittent introduction of nitric oxide into one or more parts of the system with continuous bleeding of an off-gas comprising excess nitric oxide from the system may be resorted to within the scope of the invention.

The effectiveness of nitric oxide in stabilizing unsaturated aliphatic aldehydes during conditions of transportation and/ or storage is illustrated by the following example.

EXAMPLE I Acrolein, obtained by catalytic oxidation of propylene was purified by flash distillation, and dried over anhydrous calcium sulfate. Acrolein so obtained was placed in a glass container. Nitric oxide was introduced into the container in controlled amount to result in the presence of an amount of nitric oxide equal to 0.1% by weight of the acrolein in the container. The container was then closed and stored at room temperature. The operation was repeated with the exception that nitric oxide was omitted. It was observed that the acrolein in the container containing no nitric oxide became extremely cloudy in .a period of only about 2 hours. The acrolein in the container containing nitric oxide on the other hand showed no sign of cloudiness even after a period of 9 days of storage.

A particular advantage of the nitric oxide as a stabilizer resides in its ability to suppress substantially completely the formation of the polymeric products which are relatively insoluble in the acrolein and in hydrocarbon solvents. Any polymeric material which ultimately does form after prolonged periods of storage in the presence of nitric oxide generally consists substantially exclusively of .a soluble material which not only is readily removed from thealdehyde but which does not interfere with eflicient handling, processing, or treating of the aldehyde containing it. The effectiveness of nitric oxide in suppressing the formation of the highly undesirable insoluble polyrneric material even at substantially elevated conditions of temperature is evidenced by the followingexarnple.

EXAMPLE n In operation, A, acrolein, obtained .by catalytic oxidation of propylene, purified by flash -dis tillat ion and dried over calcium. sulfate was placed in a glass container. h c n a n wa sals an stan a nt temperature of 100 C. In a second operation 13, operation A was repeated under substantially identical conditions but with the exception that nitric oxide in an amount equal to 0.1% by weight of the acrolein was introduced into the container. The operation was again repeated in an operation C under substantially identical conditions employed in B but with the exception that the acrolein contained 5% of water in addition to the nitric oxide. The operation C was repeated in an operation D under substantially identical conditions but with the exception that the acrolein contained 5% of water which had been saturated with air. Observation of the materials under the high temperature storage conditions resulted in the finding that the material stored in the operation A containing no nitric oxide became cloudy at the expiration of 15 minutes of storage. Insoluble polymer was formed at the rate of about 50% by weight of the acrolein stored per day. In operations B and C, wherein nitric oxide was present, no cloudiness was apparent even after 5 days of storage at the elevated temperature. In the operation D a slight cloudiness was apparent after 3 and /2 days of storage. In none of the operations B, C and D was there encountered the formation of insoluble polymer in detectable amounts during the period of storage.

The excellent stabilizing effect of nitric oxide upon unsaturated aliphatic aldehydes even at elevated temperatures while in contact with materials of construction normally encountered is evidenced by the following example.

EXAMPLE III Two separate batches of acrolein obtained by catalyzed oxidation of propylene, purified by a distillation and dried over calcium sulfate, were placed in containers. Nitric oxide in an amount equal to 0.1% by weight of the aerolein was introduced into the containers and the containers sealed. The two batches of acrolein were then stored in the sealed containers at C. at substantially identical conditions but with the exception that one was stored in contact with a surface of stainless steel and the other of copper. After a storage period of 5 days at the elevated temperature only a trace of cloudiness was apparent and no determinable amount of insoluble polymeric material was present in the acrolein.

Comprised within the scope of the invention is the use of the nitric oxide stabilizer in combination with agents of lesser volatility capable of functioning to some extent in suppressing the formation of gums or other resinous materials in the aldehydes during the transportation, storage or processing thereof. Such other agents employed in addition to the nitric oxide may comprise, for example, phenolic type inhibitors such as hydroquinone, 2,6-ditertiarybutyl-4-rriethyl phenol, etc. Y 'The following example is illustrative of the relative .efiiciency as stabilizer for the unsaturated aliphatic aldehydes of nitric oxide, phenolic type inhibitors, and combinations of nitric oxide with phenolic type inhibitors.

EXAMPLE IV Ten samples of a single batch of acrolein which had been obtained by the catalytic oxidation of propylene, purifiedby distillation and dried over calcium sulfate, were subjected to storage in sealed glass containers. Four of the samples were stored at a constant temperatureof 20 ,C. The other six were stored at a constant temperatureof 100 C. Stabilizing agents were added to eight of the samples as indicated in the following Table A. The stabilizing agents were added in controlled apaount to resultin an amount of the stabilizing agent in cgi 'itainer equal to 0.1% by weight of the acrolein. ,When two stabilizing agents were used in ,a single sample 0.1% by weight of each, based ,on the acrolein, was introduced into the container. Storage or eachsample was continued until a clouding became ap- Pa ent. The time elapsedfrom start of storage 'to such initial clouding noted. For the san1pl'es stored lit 100 C. the amount of polymer present was determined by evaporating the acrolein, at reduced pressure so that polymer did not form during its removal, and Weighing the resulting polymeric residue. Division of the total Weight of polymeric residue for each sample by the time of storage (in days) for that sample results in the average rate of polymer formation in terms of percent by weight per day set forth in the following Table A. Results obtained are indicated in the following Table A.

Table A Polymer Temp, Time to begin Formation Sample Agent C. Clouding Rate. percent w. per day None 20 2-3 Hrs 2,6-Di-tert. buty1-4- 20 6 Hrs methyl phenol. Hydroquinone 20 2 Days H Nitric xide 20 9 Days None 100 15 Min H 50 Hydroquinone 100 1.5 Hrs 1. 4 2,6-D1-tert-butyl-4- 100 16 Hrs 0.5

methyl-phenol. Nitric Oxide 100 Days O Nitric Oxide-l-Hydrm 100 3.5 Days 0 quinone. l0 Nitric Oxide+2,6-di 100 5 Days 0 tert. butyl-d-methyl phenol.

It is seen from the foregoing results that the addition of the phenolic agents in addition to the nitric oxide in no wise detracted from the eifectiveness of the nitric oxide in inhibiting insoluble polymer formation.

Nitric oxide, as such or in combination with other materials, is employed with particular advantage as stabilizing agent for unsaturated aldehydes during the processing or treating thereof at elevated temperatures. Its addition to the unsaturated aldehyde before subjection of the aldehyde to a process such as, for example, distillation, extractive distillation, solvent extraction or the like results in obviating to at least a substantial degree the difficulties heretofore encountered in such operations as a result of polymer deposition within the equipment employed. Heretofore, distillation of alpha-beta unsaturated aldehyde-containing mixtures, such as, for example, an aqueous crude acrolein, generally necessitated the use, in addition to a phenolic inhibitor, of relatively costly operating conditions, such as, subatmospheric pressures, refrigeration of reflux, the presence of solvents, etc. The presence of nitric oxide, it is now found, brings within the realm of practicability the distillation of such mixtures under conditions of ordinary, practical scale simple distillation. In addition to improving the chiciency of the processing or treating operation the presence of the nitric oxide results in the elimination of loss of acrolein to polymer formation and enables the production of a product possessing superior stability during subsequent transportation and storage conditions as a consequence of the presence therein of residual nitric oxide and the absence of precursors to gum formation.

EXAMPLE V In an operation, E, crude aqueous acrolein obtained by absorbing the products resulting from the coppercatalyzed oxidation of propylene in water was subjected to simple distillation in distillation equipment including a distillation column packed with ceramic packing. Distillation conditions were maintained to obtain acrolein overhead and aqueous impurities as still bottoms. Hydroquinone, in an amount equal to 0.1% by weight of the acrolein component of the feed, was added to the charge. Distillation was carried out continuously for a period of 4.2 days when extreme fouling of the equipment due to polymeric depositions made continuance of the distillation impossible. In a repetition of the operation but in the presence of nitric oxide added in an amount equal to 0.1% by weight based on acrolein content of the charge, the operation was carried on continuously for 9.6 days before any substantial polymer deposition was made apparent.

We claim as our invention:

1. The method of stabilizing an unsaturated aldehyde selected from the group consisting of acrolein and methacrolein during distillation which comprises elfecting said distillation of said aldehyde in the presence of added nitric oxide at a temperature not above about C.

2. The process for stabilizing an unsaturated aliphatic aldehyde selected from the group consisting of acrolein and methacrolein during the distillation thereof at a temperature not above 100 C. which comprises effecting said distillation of said unsaturated aldehyde in the presence of a normally gaseous stabilizing agent consisting essentially of nitric oxide in combination with a phenolic stabilizing agent.

3. The process in accordance with claim 2 wherein said phenolic stabilizing agent is hydroquinone.

4. The process in accordance with claim 2 wherein said phenolic stabilizing agent is 2,6-di-tert.butyl-4- methyl phenol.

5. The method of stabilizing an unsaturated aldehyde selected from the group consisting of acrolein and methacro-lein during distillation at a temperature not substantially above about 100 C. which comprises incorporating therewith an amount of nitric oxide ranging from about 0.001 to about 1% by weight of said aldehyde.

Briner et al.: 548.

Burnham et al.: J. Am. Chem. Soc.

62, 453 (1940). Calvert et al.: J. Chem. Physics 19, 

1. THE METHOD OF STABILIZINGAN UNSATURATED ALDEHYDE SELECTED FROM THE GROUP CONSISTING OF ACROLEIN AND METHACROLEIN DURING DISTILLATION WHICH COMPRISES EFFECTING SAID DISTILLATION OF SAID ALDEHYDE IN THE PRESENCE OF ADDED NITRIC OXIDE AT A TEMPERATURE NOT ABOVE ABOUT 100* C. 